The present invention relates generally to light fixtures. More specifically, the present invention relates to a sound absorbing light fixture for an elevator cab.
Conventional interiors of elevator cabs are made of rigid non-porous materials which absorb little or none of the sound energy which penetrates the cab. In these conventional interiors, the sound absorption coefficient, i.e., the ratio of absorbed sound energy to incident sound energy, is very low, e.g., typically less than 10%. In some prior art elevator cabs, porous materials are disposed on the interior walls to enhance the overall absorption coefficient and construct a sound energy absorbing interior which will reduce the interior noise level and improve the passengers"" ride quality.
However, optimizing the absorption coefficient of the elevator cab ceiling system is made more difficult by the lighting fixtures, which can cover over ninety percent (90%) of the interior ceiling surface. Many elevator ceiling systems are made so that solid translucent plastic sheet diffusers are placed into a light fixture frame which is suspended between the light bulb, florescent or incandescent, and the interior cab space occupied by the passengers. These solid plastic diffusers serve to shield the bright light from the passengers and spread the light more evenly throughout the interior. These covers do not have desirable acoustic properties though. The rigid non-porous diffuser reflects, rather than absorbs, most of the acoustic energy which contacts its surface.
The frames of the light fixtures are also generally constructed of rigid materials having low absorption coefficients. Moreover the space between the plastic diffusers and the frame defines an air filled cavity that will result in the formation of a standing wave pattern inside the cavity and may cause resonances at certain frequencies if not properly dampened.
There is a need therefore, for an improved light fixture for an interior such as an elevator cab.
The present invention offers advantages and alternative over the prior art by providing a sound absorbing light fixture that enhances the acoustical performance of an elevator ceiling system. The light fixture reduces interior noise and improves ride quality of an elevator system. Moreover, the light fixture can be used as a kit to retrofit existing elevator ceiling system.
These and other advantages are accomplished in an exemplary embodiment of the invention by providing a sound absorbing light fixture installed in a surface system, such as an elevator ceiling system, of an enclosed interior, such as an elevator cab. The light fixture comprises a frame disposed in fixed relationship to the surface system, the frame having an interior rear surface and interior side surfaces extending outwardly from the rear surface to define a cavity. A light source is supported by the frame within the cavity. Additionally, a light diffuser is disposed in fixed relationship to a front portion of the frame between the light source and the enclosed interior. The installed light fixture enhances a sound absorption coefficient of the surface system over a predetermined frequency range of sound energy, e.g., 100-2000 Hz.
In an exemplary embodiment of the invention, the diffuser further comprises a material having an impedance substantially matched to a redetermined percentage range of air impedance for a predetermined frequency range.
In an alternative embodiment, the cavity is sized to attenuate sound energy within a predetermined frequency range.
Additionally, in another alternative embodiment, the interior rear surface of the frame is lined with a sound absorbing material, such as acoustic foam.